Cathode-ray tube focusing device of the permanent magnet type



w. F. STEERS CATHODE RAY TUBE FOCUSING DEVICE OF THE PERMANENT MAGNET TYPE Sept. 18, 1951 3 Sheets-Sheet 1 Filed Aug. 18, 1950 l 2 7 V A Mo 0 v 00 JNVENTOR. WILLIAM F. STEERS j? me fifl ATTORNEYS Sept. 18, 1951 w F STEERS 2,568,668

CATHODE RAY TU BE FOCUSING DEVICE OF THE PERMANENT MAGNET TYPE Filed Aug. 18, 1950 3 Sheets-Sheet 2 IN V EN TOR.

WILLIAM F. STE'ERS ATTORNEYS Sept. 18, 1951 w. F. 'STEERS 2,568,668

' CATHODE RAY TUBE FOCUSING DEVICE OF THE PERMANENT MAGNET TYPE 3 Sheets-Sheet 5 Filed Aug. 18, 1950 INVENTOR. WILLIAM F. STEE R3 P QW W ATTORNEYS Patented Sept. 18, 1951 UNITED STATES PATENT OFFICE CATHODE-RAY TUBE FOCUSING DEVICE OF THE PERMANENT MAGNET TYPE Application August 18, 1950, Serial No. 180,185

3 Claims. (01. 313-84) The present invention relates to the art including cathode ray tubes such as used in television receivers or oscilloscopes and is more particularly concerned with improvements in focussing arrangements for the electron beams of such cathode ray tubes.

In the prior art it has been customary to provide focussing for cathode ray beams by use of a focussing coil surrounding the cylindrical neck of the tube and excited by direct current. This structure provides a simple means for adjusting the degree of focussing merely by adjusting the magnitude of direct current flowing in the focussing coil. However it suffers from certain disadvantages including a variation of focussing with line voltage changes, the absorption of power from the television receiver or oscilloscopes, the creation of heat dissipation problems, and an increase in costs by virtue not only of the cost of the coil itself, but the cost of the auxiliary apparatus such as a potentiometer required for adjustability, and the labor costs of assembly of all these elements.

According to the present invention these disadvantages of the use of focussing coils are substantially overcome by providing a permanent magnet type of focussing structure. According to the present invention means are provided for adjusting the degree of focussing Just as readily as in the prior art. By use of this arrangement the focussing stability is increased since focussing is no longer dependent on line voltage, the heat dissipation and power requirements are reduced, and both labor and material costs are lowered since it is no longer necessary to wire the focussing device into the circuit or to provide auxiliary adjusting apparatus.

Further objects and advantages of the invention will become more clearly apparent from the following description of preferred embodiments thereof. taken in conjunction with the appended drawings, in which- Figure 1 is a side elevation view of a cathode ray tube having one form of a permanent-magnet focussing arrangement according to the present invention mounted thereon;

Figure 2 is a longitudinal cross sectional perspective view of the focussing structure of Figure 1 showing only part of the cathode ray tube neck;

Figure 3 is an end view of a modified form of focussing arrangement;

Figure 4 is a longitudinal cross sectional view of the device of Figure 3, taken along line 4-4 thereof;

Figure 5 is a longitudinal cross sectional view of a fragmentary portion of the device of Figure 3 taken along line 8-8 thereof;

Figure 6 is a longitudinal cross sectional view of another form of focussing device according to the present invention; and

Figure 7 is a similar longitudinal cross sectional perspective view of still another form of the present invention.

Referring to Figure 1 of the drawings, there is shown a conventional cathode ray tube I having a neck portion i2, generally cylindrical in shape, and a flaring portion i2 terminating in the usual viewing screen I4. Placed around the cylindrical neck l2 of the tube Ii is a permanent magnet type of focussing arrangement i6 according to one form of the present invention.

As shown more fully in Figure 2 this iocussing arrangement It has a mounting plate ll of generaliy circular or any other preferred shape surrounding the neck i2 of the tube. Mounting plate I! is adapted to be secured in any suitable manner to a frame or chassis for supporting the foeussing arrangement l6. Suitably fastened to the mounting plate I1 is an end ring l8 of magnetic material, it being understood that the mounting plate II is preferably of non-magnetic material, such as aluminum, brass or the like. Ring I! has a central aperture adapted to accommodate the neck i2 of the tube ii.

A cylindrical magnet I8 is arranged coaxially with respect to plate i1 and ring i8, being held in place by a second magnetic ring 2| and suitable fastening means, such as rods 3!. Ring 2| is internally threaded, and is threadedly engaged with an outwardly threaded cylinder 22 of magnetic material. Cylinder 22 is fixed to a disc 23 serving as a drive member for rotating the threaded cylinder 22, as by means of a suitable friction drive indicated schematically at 24, having a. rotatable control shaft 26 to which is fixed drive members 21 frictionally engaging the disc 23. The shaft 26 may be extended to form a. guide 28 sliding within a tubular member 29 fixed to plate H, for purposes of support and alignment.

It will be thus seen that the magnetic members l8 and i8, 2i and 22 provide a nearly closed path for the magnetic field except for the gap 32 between the threaded cylinder 22 and the end ring i8, and this gap 82 is adjustable by means of the friction drive 2|. By adjusting the length of the gap 22 any desired value of magnetic field intensity can be obtained within the tube ll, thereby providing a readily adjustable permanetic plate 34 and a further magnetic plate 36 are a plurality of permanent magnets ill; A magnetic cylinder 31 is slidably retained within the central aperture of magnetic plate 36 and is axially adjustable with respect to the tube II by means or a suitable drive shown in Figure 5, comprising a threaded shaft 38 threadedly engaged in lugs 39 afilxed to the cylinder 31, the shaft 38 passing freely through an opening 4| in the plate 36 and being rotatably seated in mounting plate 33, as at 42. It will be understood that any other suitable means ior conveniently axially adjusting the cylinder 31 may also be utilized.

In this form of the invention also, magnetic members 34, 36 and 31 form a complete magnetic pole piece structure for the focussing arrangement, providing a gap 43 which is conveniently adjustable to adjust the magnetic field within the tube II and thereby adjust the focusslng eflect. As before the field is circularly symmetrical by virtue of the cylindrical member 31 and the circularly apertured magnetic pole piece 34. In this instance the mounting plate 33 and plates 34 and 36 are shown as generally triangular in shape, which may 'be a convenient shape for physically mounting the apparatus on a chassis or the like, However it will be understood that in this and other forms of the invention any desired shape may be utilized so long as a properly symmetrical and adjustable permanent magnet field is provided.

Figure 6 shows a form of the invention using a cylindrical permanent magnet 6| with an ad- Justable cylindrical magnetic shunt 62 exterior thereto. For the purpose of permitting adjustable positioning oi either the magnet 6| or the shunting cylinder 62, there are provided a plurality of tapered cylindrical non-magnetic members 63, 64, 65 and 66. It will be understood that the members 63 and 66 taper oppositely, as do the members 64 and 65. The magnet 6| is first positioned on the tube neck as desired, and is then maintained in position by pressing the tapered cylinders 63, 66 in opposite directions toward one another so as to wedge themselves together within the magnet 61 which is thereby held in suitable position. Similarly, the shunting cylinder 63 is held in position relative to the magnet 6| by similar wedging action of the tapered cylinders 66 and 64. One of these cylinders, such as 63 or 66, may be suitably mounted on a mounting plate where desired in order to center the entire structure with respect to the tube axis.

Figure 7 shows another form of the present invention. In this case a non-magnetic mounting bracket 1| is provided having a disc portion 12 and a cylindrical portion ,13. mounted on the cylindrical portion 13 is the adjustable magnetic sleeve or cylinder 14. Fixed to the disc portion 12 is a magnetic end plate 16, apertured to receive the tube neck l2. Fastened between the end plate 16 and a second magnetic end plate 11 are the bar type permanent magnets 18, two of which are shown in Figure 9,. although it will be understood that a larger plurality will generally be utilized to provide a symmetrical magnetic field. Magnetic sleeve 14 is axially ad- Justable by means of the control member 19' con- Slidably 4 pied to a flexible shaft 8i terminating in a threaded member 82 which is rotatably se'ted in the mounting plate II as at 83. Threded member 82 is threadedly engaged with a .ug or bracket 84 formed on the adjustable sleeve 14 so that, upon rotation of the control 19, the threaded members 82, B-B'cause the sleeve 14 to advance in the selected direction along the tube neck 12. For the purpose of centering the entire structure relative to the axis of the tube, an adjustable pole plate 86 is provided which is in magnetic contact with plate 16 and has an inwardly turned flange 81; Plate 86 is rotatably mounted eccentrically with respect to the tube I2. A centering rod 88 is provided which passes freely through an aperture 89 in the extension 9| of pole plate 11 and also into an aperture 92 in plate 86. By using the aperture 89 as a fulcrum for the rod 88 the plate 86 can be rotated with respect to the axis of the tube, thereby changing the axial relationship of the flange 81 with respect to the axis of the tube. This varies the axial distribution of magnetic field and thereby overcomes any undesired asymmetry. Normally this would be adjusted to center or otherwise set the electron beam spot with respect to the screen l4 of the tube. The adjustable pole plate 86 is suitably held to the fixed plate 16 by spring tension and magnetic force. The adjustment of control 16 then varies the gap between flange 81 and sleeve 14 to vary the intensity of the magnetic field for focussing.

Accordingly in each of the forms of the present invention there has been illustrated a permanent magnet type of iocussing device requiring noenergization and yet permitting full symmetrical and adjustable focussing control. It will be understood that in all of the above forms of the invention bar magnets may be replaced by cylindrical magnets, or vice versa, so long as proper symmetry is maintained. Also the entire unit may be supported in any desired manner either from the chassis or cabinet of a television set, oscilloscope or the like, wherever such a tube may be utilized.

It will be understood that in any of the above forms of invention any other desired form of mechanical drive for the adjustable sleeve may be used. Thus, in Fig. 2, in place of the friction drive 24, plate 23 may be formed as a gear, and an elongated spur gear pinion in mesh therewith may be mounted on shaft 26. Alternatively. a sprocket may be formed or fixed on plate 23, and a corresponding sprocket fixed to shaft 26, with a. chain drive extending in engagement therewith. Other equally eiiective arrangements can be readily conceived.

What is claimed is:

1. A permanent magnet focussing device for cathode ray tubes, comprising a pair of centrallyapertured magnetic pole plates to surround the neck of a cathode ray tube, and arranged to extend radially from the axis-thereof, an axially symmetrical permanent magnet sleeve extending between said pole plates, an inner magnetic sleeve within said arrangement extending coaxially with the tube opening from one 'of said pole plates to a plane adjacent to the other pole plate to define a magnetic circuit including an air gap formed by said sleeve and said pole plate, and means for axially adjusting said inner magnetic sleeve, comprising a non-magnetic plate on said sleeve paralleling said magnetic pole plates and a clutch engaging said plate and said first magnetic pole plate whereby relative movement of aueaoes 5 said sleeve between said plates to vary the width of the said air gap may be accomplished.

2. In the apparatus in accordance with claim 1, the clutch including an internally threaded element fixed to said sleeve and a rotatable and nontranslatable screw member engaged within said threaded element whereby upon rotation thereof said sleeve is correspondingly moved.

3. A permanent magnet focussing device for cathode ray tubes, comprising a pair of centrally apertured magnetic pole plates adapted to surround the neck of a cathode ray tube and extending radially from the axis thereof, an axially symmetrical permanent magnet arrangement extending between said pole plates, a magnetic sleeve inside said arrangement extending axially within one of said pole plates and adjacent the other to form a gap between one end of said sleeve and the edge of the aperture of said other pole plates, said sleeve being axially adjustable to adjust the size of said gap, and an internally threaded element fixed to said sleeve with a rotatable and non-oscillatable screw member engaged within said threaded element whereby upon rotation of said screw member said sleeve is longitudinally moved.

WILLIAM F. STEERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,200,039 Nicoll May '7, 1940 2,212,206 Holst et a1. Aug. 20, 1940 2,234,720 De Tar Mar. 11, 1941 2,259,531 Miller et a1. Oct. 21, 1941 2,336,837 Bedford Dec. 14, 1943 2,416,687 Fry Mar. 4, 1947 2,418,487 Sproul Apr. 8, 1947 2,431,077 Poch Nov. 18, 1947 2,442,975 Grundmann June 8, 1948 2,533,687 Quam Dec. 12, 1950 2,533,688 Quam Dec. 12, 1950 2,533,689 Quam Dec. 12, 1950 FOREIGN PATENTS Number Country Date 462,683 Great Britain Mar. 12, 1937 472,165 Great Britain Sept. 13, 1937 521,439 Great Britain May 22, 1940 597,255 Great Britain Jan. 21, 1948 615,553 Great Britain Jan. 7, 1949 

